1. Field of the Invention
The present invention relates to liquid crystal displays. More specifically, the present invention is directed to a flat fluorescent lamp, characterized by inducing a discharge even at a low discharge initiating voltage, minimizing a non-luminescent region, and maintaining an optimal luminance uniformity, whereby the flat fluorescent lamp has a uniform screen brightness; and a backlight unit using the same.
2. Description of the Related Art
In general, a flat-panel display is classified into a light-emitting type, such as CRT (Cathode Ray Tube), FED (Field Emission Display), PDP (Plasma Display Panel) and organic EL (Electro Luminescence), and a light-receiving type, for example, LCD (Liquid Crystal Display). Of them, the liquid crystal display has no light-emitting structure, and cannot display an image unless light is externally irradiated. Hence, an additional light source, for example, a backlight unit, should be employed to display the image.
Such a backlight unit utilizes a manner of fabricating a planar light source by converting light irradiated from CCFL (Cold Cathode Fluorescent Lamp) through a light plate, or by disposing a plurality of CCFLs onto a rear surface of a liquid crystal panel, or by placing a discharge gas and a fluorescent material between flat glass plates to cause a discharge.
In particular, a flat fluorescent lamp, which is the manner of fabricating a planar light source by placing a discharge gas and a fluorescent material between flat glass plates to cause a discharge, is composed of a discharge electrode structure attached to a front substrate or a back substrate while the discharge gas including xenon (Xe) and neon (Ne) is filled in a discharge channel between the front and back substrates coated with the fluorescent material as the two flat glass plates.
Upon application of power to the discharge electrode of the above flat fluorescent lamp, while the fluorescent layer is excited by ultraviolet light caused by a gas discharge between the discharge electrodes and then converted to a stable state, visible light is generated (surface light emission), thereby realizing the image of the liquid crystal display.
However, the conventional flat fluorescent lamp, as mentioned above, is disadvantageous in terms of a short electrode spacing, and a low ultraviolet light emission efficiency of the discharge gas. On this account, a conversion efficiency of the ultraviolet light to the visible light amounts to 30 lm/W at the most. Hence, to increase the above conversion efficiency, there is required a high driving power. So high a driving power leads to an increased power consumption, whereby power loss is caused. After all, the conventional flat fluorescent lamp suffers from the generation of tremendous heat.
Proposed to increase a light efficiency, a flat fluorescent lamp includes a discharge channel having a serpentine shape that is formed between a front substrate and a back substrate as two flat glass plates, and an electrode disposed at each of a starting point and an ending point of the serpentine type discharge channel, which has reference to FIG. 1. Such a flat fluorescent lamp, having one discharge channel, allows a large quantity of current to flow in the relatively long discharge channel, thus enhancing the light efficiency.
However, the above flat fluorescent lamp is disadvantageous in that the long discharge channel requires a high discharge initiating voltage, and then a high driving voltage. After all, a current leakage increases. Further, although there is necessary a flat fluorescent lamp having a drastically lengthened serpentine channel according to the fabrication of large-sized LCDs and backlight units in recent years, it is impossible to commercially manufacture such a flat fluorescent lamp.
To solve the problems, Korean Patent Laid-open Publication No. 2001-0079377 discloses a flat fluorescent lamp and a fabrication method thereof. The disclosed fabrication method of the flat fluorescent lamp includes steps of heating a flat glass plate to predetermined molding temperatures, molding the heated flat glass plate by use of a mold processed to have a plurality of discharge channels defined by partitions and communicated with each other through discharge passages, to prepare a molded flat glass plate having discharge channels, removing the molded glass plate from the mold, slowly cooling the molded glass plate, coating a fluorescent material to the insides of the discharge channels of the molded glass plate, followed by a burning process, attaching the glass plate to a front cover through a sealing frit, removing air from the insides of the discharge channels of the glass plate, introducing a discharge gas into the discharge channels, closing exhaust ports of the discharge channels, and mounting an electrode to apply a high frequency power to the discharge channels. The flat fluorescent lamp fabricated like this has an electrode structure of inner electrodes disposed to both ends of the discharge channels or strip-shaped outer electrodes disposed at both lateral surfaces of the discharge channels. However, the flat fluorescent lamp having the above discharge electrode structure suffers from crosstalk between discharge channels, which causes a strong discharge in a specific discharge channel among the discharge channels or a very unstable plasma discharge, upon the discharge by application of the power. This causes differences between strengths of electric field of the discharge channels, resulting in a non-uniform luminance. Eventually, the flat fluorescent lamp has a non-uniform screen brightness.
This is because large quantities of discharge currents gather in the specific discharge channel where the discharge relatively easily occurs while discharge charges are freely transferred to the neighboring discharge channels through the discharge passages.